1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and an electrophotographic apparatus. The present invention specifically relates to an electrophotographic photosensitive member which has a photoconductive layer formed from hydrogenated amorphous silicon, and has an intermediate layer and a surface layer both of which are formed from hydrogenated amorphous silicon carbide, on the photoconductive layer. Hereinafter, the hydrogenated amorphous silicon is referred to as “a-Si” as well, and the hydrogenated amorphous silicon carbide is referred to as “a-SiC” as well. In addition, the surface layer formed from “a-SiC” is referred to as “an a-SiC surface layer” as well.
2. Description of the Related Art
An electrophotographic photosensitive member is known, which has a photoconductive layer (photosensitive layer) formed from an amorphous material on a substrate. An amorphous-silicon electrophotographic photosensitive member (hereinafter is referred to as “an a-Si photosensitive member” as well) has already been commercialized, which has a photoconductive layer formed on the substrate with a layer-forming technology such as a chemical vapor deposition method (CVD method) and a physical vapor deposition method (PVD method), in particular. The layer structure of the a-Si photosensitive member is a layer structure as is illustrated in FIG. 5, for instance. In FIG. 5, an electrophotographic photosensitive member 5000 has a photoconductive layer 5002 formed from a-Si (hereinafter referred to as “an a-Si photoconductive layer” as well) formed on an electroconductive substrate 5001, and an a-SiC surface layer 5005 formed on the photoconductive layer 5002. The a-SiC surface layer 5005 is an important layer relating to electrophotographic properties. The properties required to the surface layer of the electrophotographic photosensitive member include abrasion resistance, moisture resistance, charge retentivity and optical transparency. The a-SiC surface layer has been mainly used for an electrophotographic apparatus having a quick process speed, because of being particularly superior in abrasion resistance and also superior in the balance among the above described other properties.
However, a conventional a-SiC surface layer has occasionally caused an image deletion (hereinafter referred to as “high-humidity deletion” as well) when having been used in a high-humidity environment. The high-humidity deletion means such an image failure that letters are blurred or form a white patch without being printed, occurring when an image has been repeatedly formed in the high-humidity environment according to an electrophotographic process and an image is output again after a while. One cause of this phenomenon is moisture which has adsorbed onto the surface of the electrophotographic photosensitive member. Conventionally, in order to reduce the occurrence of the high-humidity deletion, it has been conducted to always heat the electrophotographic photosensitive member with a heater for the photosensitive member, and reduce or remove the moisture which has adsorbed onto the surface of the electrophotographic photosensitive member. Such an electrophotographic photosensitive member is also proposed as to reduce the high-humidity deletion by other methods than the method using the heater for the photosensitive member.
Japanese Patent No. 3124841 discloses a technology of setting the atom density of a silicon atom, a carbon atom, a hydrogen atom or a fluorine atom in an a-SiC surface layer at a smaller value than a predetermined value, in an a-Si photosensitive member which has a photoconductive layer and the a-SiC surface layer sequentially formed on a substrate. The technology in Japanese Patent No. 3124841 forms the a-SiC surface layer so as to have a comparative rough layer structure by setting the atom density of each atom constituting the a-SiC surface layer at a smaller value than the predetermined value, and facilitates the a-SiC surface layer to be abraded in a cleaning step of the electrophotographic process. Japanese Patent No. 3124841 describes that the technology thereby acquires a new surface which always contains a little amount of the adsorbing moisture and thereby can reduce the high-humidity deletion. A technology is also proposed which relates to the enhancement of characteristics of the electrophotographic photosensitive member by improving the a-Si photoconductive layer and the a-SiC surface layer in the a-Si photosensitive member.
Japanese Patent No. 3236692 describes a technology of setting an atom density of atoms in an amorphous state in each layer at a smaller value than a predetermined value, and setting an atom density of the atom which compensates a dangling bond at a larger value than a predetermined value, in an electrophotographic photosensitive member which has a carrier injection inhibition layer, a photosensitive layer and a surface layer sequentially stacked on a substrate. Japanese Patent No. 3236692 describes that such layers can be stacked as to have layer thicknesses necessary for securing the abrasion resistance while improving charge transportability and preventing the increase of the residual potential by increasing defect density in the top surface side. The Patent also describes that charge retentivity can be secured at the same time by decreasing the defect density of the surface layer in the photoconductive layer side.
Japanese Patent Publication No. H05-018471 proposes an electrophotographic photosensitive member in which an a-SiC surface layer has been two-layered, in the a-SiC photosensitive member which has an a-Si photoconductive layer and an a-SiC surface layer sequentially formed on a substrate. Japanese Patent Publication No. H05-018471 discloses a technology of forming the a-SiC surface layer in which the defect density of the surface layer in the top surface side out of the two-layered surface layers is higher than that of the surface layer in the photoconductive layer side. Japanese Patent Publication No. H05-018471 describes that such surface layers can be formed as to have layer thicknesses necessary for securing the durability because the increase of the residual potential can be reduced by increasing the defect density in the top surface side. Japanese Patent Publication No. H05-018471 also describes that as a result, an electrophotographic photosensitive member having superior electrical properties can be produced by consequently making the a-SiC surface layer as a layer structure which has a high defect density and is comparatively rough.
Japanese Patent No. 3152808 describes a technology of setting an atom density of atoms in an amorphous state for skeleton constituting the photoconductive layer at a larger value than a predetermined value, and setting the atom density of the atom for compensating a dangling bond at a small value, when using an image exposing source having a wavelength of a predetermined wavelength or less. By thus setting the atom density of the atoms in an amorphous state for the skeleton constituting the photoconductive layer at the predetermined value or larger, a distance between each bonded atom is shortened, and accordingly a band gap as required can be obtained. In addition, by setting the atom density of the atom for compensating the dangling bond at the small value, a photocarrier exceeding the band gap can be generated with respect to a light amount of high-energy light having a predetermined wavelength for image exposure or shorter, and the carrier can be conducted through the band conduction of the generated carrier at high mobility. Japanese Patent No. 3152808 describes that as a result, the chargeability increases, an exposure potential is lowered, and an electrophotographic photosensitive member which can reduce the occurrence of an afterimage can be produced.
In recent years, it is required for an electrophotographic process to satisfy power-saving properties as well from the viewpoint of environmental consideration, while satisfying requests for a higher speed, a higher image quality and the longer life. In other words, further improvement is desired to the electrophotographic photosensitive member. For instance, as for the moisture resistance, if the high-humidity deletion occurs, the image quality decreases. Accordingly, an electrophotographic photosensitive member is required which does not cause the high-humidity deletion even in the high-humidity environment and can keep a high image quality. Here, when the above described heater for the photosensitive member is installed so as to keep the high image quality in the high-humidity environment, an electric power corresponding to a standby power is needed even when the electrophotographic apparatus is not operated, which makes it difficult to improve the power-saving properties.
In addition, even when the technology disclosed in Japanese Patent No. 3124841 is employed, the surface of the electrophotographic photosensitive member needs to be scraped off at some abrasion rate, and accordingly, an electrophotographic apparatus having a quick process speed, in particular, does not sufficiently secure the durability of the electrophotographic photosensitive member, occasionally. The factor because of which the durability of the electrophotographic photosensitive member cannot be sufficiently secured includes layer exfoliation in addition to the above described abrasion of the surface. When the layer thickness of the a-SiC surface layer is increased to a degree of being capable of coping with the request for the longer life, the internal stress of the surface layer increases. When the internal stress of the surface layer increases, there has been the case of causing the layer exfoliation in the vicinity of the interface between the photoconductive layer and the a-SiC surface layer, when a sudden environmental change (sudden change in temperature, humidity and the like) has occurred. One example of the cases in which such a sudden environmental change occurs includes the transportation of the electrophotographic photosensitive member by an aircraft.
The reason of causing the layer exfoliation in the vicinity of the interface between the photoconductive layer and the a-SiC surface layer is considered to be because when the internal stress of the a-SiC surface layer increases, a difference of the internal stress between the photoconductive layer and the a-SiC surface layer is expanded, and the stress is concentrated in the vicinity of the interface between the two layers. It is possible to alleviate the stress concentration in the vicinity of the interface between the photoconductive layer and the a-SiC surface layer by providing an intermediate layer between the photoconductive layer and the a-SiC surface layer, so as to reduce the layer exfoliation in the vicinity of the interface between the photoconductive layer and the a-SiC surface layer. However, when the surface layer having a large internal stress has been used, even though the above described intermediate layer was provided, there has been the case in which the interface between the photoconductive layer and the intermediate layer cannot withstand the high stress received from the surface layer, and the layer exfoliation occurs in the vicinity of the interface.
In addition even if the layer exfoliation in the vicinity of the interface between the photoconductive layer and the a-SiC surface layer is reduced by providing the intermediate layer, there has been the case of causing the layer exfoliation due to the fracture of the photoconductive layer when a sudden environmental change has occurred. The reason why the layer exfoliation is caused by the fracture of the photoconductive layer is considered to be because the occurrence of the layer exfoliation in the vicinity of the interface between the photoconductive layer and the a-SiC surface layer is reduced by providing the intermediate layer and thereby the stress coming from the surface layer concentrates in the photoconductive layer itself.